What do /a/ and /O/ merge to?

[Herbert Stahlke]

When I talk about the /a/~/O/ merger in various of my classes I fairly
regularly find that among students who merge them, some merge to /a/ and
others to /O/.  Based just on observing my students, it appears that
students from southern Indiana, south of Indianapolis, who merge are like to
merge to /O/.  Students from north of Indy merge to /a/.  But I haven't
collected specific data on this.  I've looked through the discussion on the
Phonological Atlas of North America site, although I haven't read closely
the newly revised Chapter 11 that has to be the most extensive treatment of
the merger anywhere.  However, I haven't come across the question of what
they merge to.  Has anyone investigated this?

Herb